The Operation of a Transformer

Q1. Which statement correctly completes the description of how a transformer works? A transformer works by electromagnetic induction. An alternating current in the primary coil produces a ______ magnetic field in the core, which induces an emf in the secondary coil.

Multiple Choice · 1 point

• · constant
• · alternating
• · zero
• · decreasing only

Q2. Which statement correctly completes the description? The changing magnetic flux in the core induces an ______ in the secondary coil.

Multiple Choice · 1 point

• · electric field
• · emf
• · current directly
• · force

Q3. Which statement correctly completes the description? The size of the output voltage depends on the ratio of the number of ______ in the primary and secondary coils.

Multiple Choice · 1 point

• · charges
• · electrons
• · turns
• · wires

Q4. Put the stages of energy transfer in a transformer in the correct order.

Ordering · 3 points

• 1. Alternating current flows in the primary coil
• 2. Changing magnetic flux is produced in the core
• 3. An emf is induced in the secondary coil
• 4. Electrical energy is transferred to the load

Q5. Explain how a transformer transfers energy from the primary coil to the secondary coil.

Long Answer · 3 points

Q6. A transformer steps down voltage from 240 V to 12 V. A device connected to the secondary draws 3.0 A. The transformer operates at 75% efficiency. What is the input current?

Multiple Choice · 1 point

• · 0.20 A
• · 0.50 A
• · 0.13 A
• · 0.90 A

Q7. A transformer has 1200 turns on the primary and 300 turns on the secondary. It is connected to a 240 V supply. The primary current is 2.0 A and the transformer is 80% efficient. What is the output power delivered to the load?

Multiple Choice · 1 point

• · 480 W
• · 384 W
• · 96 W
• · 240 W

Q8. A power station transmits 25 MW of power using a transformer that steps up voltage from 20 kV to 400 kV. Assuming the transformer is ideal, what is the current in the transmission lines?

Multiple Choice · 1 point

• · 62.5 A
• · 125 A
• · 31.25 A
• · 250 A

Q9. A transformer steps up voltage from 6.0 kV to 120 kV. The primary current is 12 A and the secondary current is 0.50 A. What is the efficiency of the transformer (to 3 significant figures)?

Multiple Choice · 1 point

• · 83.3%
• · 100.0%
• · 72.0%
• · 90.0%

Q10. A transformer has 1000 turns on the primary and is connected to a 240 V supply. It supplies 480 W to a load at the secondary, and the secondary current is 4.0 A. The transformer efficiency is 80%. How many turns should the secondary coil have?

Multiple Choice · 1 point

• · 625 turns
• · 1000 turns
• · 500 turns
• · 250 turns

Q11. A transformer has 500 turns on the primary and 50 turns on the secondary. The secondary provides 1.2 kW to a load drawing 6.0 A. What is the required primary (supply) voltage?

Multiple Choice · 1 point

• · 2.00 kV
• · 200 V
• · 20.0 kV
• · 2.00 V